The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicle control systems such as engine and transmission control systems use electrical, electro-mechanical, hydraulic and pneumatic devices to monitor operating conditions and to adjust operation. The speed of controlling the devices and the complexity of their operation has significantly increased. The vehicle control systems usually include diagnostic systems that determine whether the devices are functioning according to design. Demands on the diagnostic systems have increased as the vehicle control systems have become more complex.
The performance requirements of a particular output device or input signal for the vehicle control system may vary. For example, the diagnostic system may be required to detect and respond to an electrical fault of a first device or first input signal in less than 50 milliseconds to maintain control of the system. Other devices and/or input signals may allow diagnosis over longer or shorter intervals. The diagnostic system needs to detect and respond to a critical fault to correctly manage the failure mode to minimize damage and maximize safety.
Most diagnostic systems are designed to detect and respond to continuous faults that are present for predetermined time periods, for example 5 seconds or longer. The diagnostic systems set a Diagnostic Trouble Code (DTC) to inform the operator that a failure has occurred and that the vehicle requires service. When the DTC is set, the diagnostic system performs failure mode management to protect the system or subsystem. The action taken at the time the DTC is set is referred to as a permanent default action. The permanent default action is performed as long as the DTC is set.
Requiring the fault to be continuous and present for longer periods of time (for example only, 5 to 10 seconds) allows the diagnostic system to reduce false failures. A false failure occurs when the diagnostic system indicates a fault is present when no actual fault is present. Another type of false failure occurs when the diagnostic system sets a DTC too quickly and the vehicle is taken in for service the fault is no longer present. This condition is typically caused by a fault that is intermittent. These faults may significantly increase warranty costs and decrease customer satisfaction.
Vehicle control systems may be required to detect and respond to electrical faults that exist for very short periods of time to maintain control of a complex system. When these faults are detected, an appropriate failure mode management action may be performed. Therefore, diagnostic systems may be required to detect both continuous and intermittent faults. Intermittent faults can be short in duration, random, erratic, non-repeatable and/or repeatable.
Requiring detection and response to intermittent faults may increase false passes and/or false failures. False passes occur when the diagnostic system indicates no fault is present when a fault is actually present. False passes prevent failure mode management action by the diagnostic system. Therefore, accurate detection and response to various intermittent electrical faults will reduce false passes. Detecting random, short intermittent faults may also increase false failures.